Project Summary Tuberculosis kills over 1 million people a year, and an increasing percentage of these cases involves bacteria that are resistant to all front line and many second line therapies. New drugs and new drug targets are needed to combat the relentless evolution of resistance. We have discovered a scaffold, which we designate Q, that has potent in vitro antibacterial activity against Mtb. These compounds are active in macrophage infections and do not display host cell cytotoxicity. Some Q compounds inhibit the essential enzyme inosine monophosphate dehydrogenase 2 (MtbIMPDH2), but other closely related compounds engage an unknown target. Multi-target antibiotics have a greatly diminished risk of developing resistance than single target compounds, so the observation that the structure-activity relationship (SAR) of MtbIMPDH2 inhibition overlaps with inhibition of another essential enzyme is exciting. Indeed, we have as yet been unable to generate strains that are resistant to these compounds. Here we propose to further interrogate the SAR of antimycobacterial activity and to identify the unknown target using a multi-pronged approach. These experiments will lay the foundation for the development of multitarget antibiotics that will be ?resistance-resistant?.